Should I choose a pump?

Insulin Pump for Beginners

Content

• Chapter 1: Insulin Pump and Continuous Glucose Monitoring System (CGMS)
• Chapter 2: What is a Hybrid / partially-closed loop system?
• Chapter 3: How does an Insulin Pump deliver insulin?
• Chapter 4: Pre-meal bolus insulin dose
• Chapter 5: Special bolus types
• Chapter 6: Low suspend function
• Chapter 7: What is active insulin time / insulin on board?
• Chapter 8: Real-life example 1: Persistent high glucose level after lunch
• Chapter 9: Real-life example 2: Low glucose level after correction dose
• Chapter 10: Real-life example 3: High glucose overnight
• Chapter 11: Exercise tips
• Chapter 12: Tips for using an Insulin Pump and CGMS
• Chapter 13: Potential advantages and disadvantages of an Insulin Pump
• Chapter 14: Message to parents

Chapter 1: Insulin Pump and Continuous Glucose Monitoring System (CGMS)

Insulin pump

• An insulin pump is an electronic device that delivers insulin.
• Users need to input a programmed calculation system, blood glucose readings and the amount of carbohydrate to be consumed. The insulin pump will then calculate the amount of bolus insulin to be delivered based on the pre-set programme.
• It usually communicates with CGMS.

An insulin pump set includes:

• A pump: A small machine that contains user interface and electronic processor
• A disposable insulin reservoir and a disposable infusion set (to be changed every 3 days usually)

Continuous Glucose Monitoring System (CGMS)

• A device inserted under the skin to measure interstitial glucose level continuously.
• Sensor glucose may be different from blood glucose because it measures glucose in interstitial fluid.
• There is a lag time of 5-10 minutes between sensor glucose and blood glucose.

A CGMS measures interstitial fluid glucose continuously so there is a better idea on the glucose trend. It can be used as a standalone device or in combination with an Insulin Pump.

Chapter 2: What is a Hybrid / partially-closed loop system?

Currently, most computer algorithm available on the market can only automatically determine the basal insulin dose based on glucose measurement by CGMS. For the bolus insulin dose, users are still required to enter the carbohydrate portions and give meal bolus. Therefore, it is still a hybrid / partially closed-loop system.

Consist of 3 components:

• Continuous Glucose Monitoring System (CGMS)
• Computer algorithm: Automatically calculates the basal and bolus insulin dose based on glucose measurement by CGMS
• Insulin pump: Delivers insulin.

Communication between the CGMS, insulin pump and computer algorithm will create a partially-closed-loop system that can automatically adjust the rate and deliver insulin.

Chapter 3: How does an Insulin Pump deliver insulin?

Basal insulin

• Users only need a rapid-acting insulin (e.g. Aspart or Lispro) which is delivered continuously via the pump to replace long-acting insulin.
• Since our body requires different amounts of basal insulin at different times of a day, basal insulin can be delivered at variable rates by the pump.

Bolus insulin

• Cover carbohydrate intake
  • Users have to enter the amount of carbohydrates they are going to consume; the pump will release a corresponding dose of bolus insulin to match the rise of glucose.
• Correct high blood glucose
  • When the blood glucose reading is higher than target level, users have to enter the current blood glucose level, then the pump will calculate the correction dose.

Insulin-Carbohydrate Ratio (ICR):

• For calculation of food bolus
• The amount of Carbohydrates (CHO, in grams) that are covered by 1 unit of insulin
• Example: ICR 10 means 1 unit of insulin will cover 10g of CHO

Insulin-Sensitivity Factor (ISF):

• For calculation of correction bolus
• The drop in blood glucose level
• Example: ISF 4 means 1 unit of insulin will lower blood glucose by 4 mmol/L

Chapter 4: Pre-meal bolus insulin dose

Food Bolus Dose + Correction Bolus Dose = Total pre-meal bolus insulin dose

• Food Bolus Dose = CHO (g) ÷ ICR
• Correction Bolus Dose = (Current BG - Target BG) ÷ ISF

Example

• Plan to take 40g of carbohydrates
• Current BG: 17.2mmol/L
• BG target: 5.6mmol/L
• Pump settings:
  • Insulin-to-carb-ratio (ICR): 10
  • Insulin sensitivity factor (ISF): 8
• Total pre-meal bolus insulin dose = (40 ÷ 10) + [(17.2 - 5.6) ÷ 8] = 5.5 units

Chapter 5: Special bolus types

Normal bolus

• How it works: Provides a single immediate dose of insulin
• When to use it:
  • To cover carbohydrate intake with low fibre, low protein or low fat
  • To correct a high blood glucose reading

Square wave

• How it works: Delivers a single bolus evenly over an extended period of time (30 minutes to 8 hours)
• When to use it:
  • Conditions which require longer digestion or having delayed absorption (Meals with low carbohydrate but with high fat content)
  • Extended meal time (e.g. hotpot, barbeque...)

Dual wave

• How it works:
  • Delivers an immediate 'Normal' bolus followed by a 'Square Wave' bolus
  • Normal bolus can cover immediate rise of blood glucose whereas the Square Wave can cover the delayed rise of blood glucose
• When to use it: Meals that are both high in carbohydrates and fat (e.g. Pizza) as its high fat content may delay digestion

Chapter 6: Low suspend function

Suspend on low

• The pump will temporarily stop delivering insulin if sensor glucose has reached or fallen below the low pre-set limit.

Suspend before low

• The pump will temporarily stop delivering insulin if sensor glucose is predicted to reach or fall below the low limit in 30 minutes.

Chapter 7: What is active insulin time / insulin on board?

• After a bolus is given, the amount of insulin that is 'active' in our body drops with time and reaches zero at the time set by the duration of 'active insulin time' value.
• The Pump's bolus calculator approximates this drop in insulin by calculating an 'insulin on board' (IOB) or 'active insulin' value.
• For example, if your duration of 'active insulin time' is 4 hours and a bolus of 8 units was given at 8am, the IOB amount decreases steadily over time
• The IOB amount decreases 2 units per hour and has returned to zero after 4 hours (i.e. 12noon).

Chapter 8: Real-life example 1:

Persistent high glucose level after lunch (indicates inadequate bolus insulin)

• Ching Ching took 60g CHO for lunch, her pre-lunch BG was 6.5mmol/L, glucose level rose to 13mmol/L after 2 hours.
• Solution: Adjust ICR from 15 to 12, insulin dosage increased from 4u to 5u.
• Target range: blood glucose increases by around 2-3mmol/L at post-meal 2-3 hours.
• For illustration only, all dosage changes should be advised by medical team.

Chapter 9: Real-life example 2:

Low glucose level after correction dose (indicates excessive correction bolus)

• Long Long's current BG was 14mmol/L, and target BG was 5.6mmol/L. After correction, BG drops to 3.2mmol/L.
• Solution: Adjust the ISF from 4 to 5, less insulin would then be given (from 2.1u to 1.7u) to avoid excessive correction and low blood glucose.
• Note: no ISF adjustment would be needed / allowed if using hybrid-closed loop system
• For illustration only, all dosage changes should be advised by medical team.

Chapter 10: Real-life example 3:

High glucose overnight (indicates inadequate basal insulin rate)

• Ying Ying experienced high glucose overnight.
• Solution: Raise the basal insulin rate from 0.7u per hour to 0.8u per hour, in order to keep overnight glucose level in the target range.
• Note: No basal rate adjustment would be needed / allowed if using hybrid-closed loop.
• For illustration only, all dosage changes should be advised by medical team.

Chapter 11: Exercise tips

1. Close monitoring of sensor glucose during exercise.
2. For water sports: do not disconnect insulin pump for more than 1 hour.
3. Temporary target
   • For patients using the hybrid-closed loop system, a temporary target can be set at a higher level (e.g. 8.3 mmol/L) during exercise.
   • You can also consider setting the higher temporary target for a longer period (possibly overnight) or consume extra carbohydrates for intense / long duration of exercise.
   • Depending on the intensity and duration of exercise, you may set the higher temporary target before exercise starts.
4. Temporary basal rates
   • During exercise, a temporary basal rate can be set to stabilise blood glucose levels.
   • Temporary basal rate can be set for 30 minutes to 24 hours. It will automatically return to original basal rate afterwards.
   • Temporary basal rate can be set 30 minutes before exercise starts, depending on the exercise intensity.
   • Note: For hybrid-closed loop system users, temporary basal rate is not needed
5. If lows persist even with use of temporary target, consider suspending the pump for part of the exercise time, or change to manual mode with temporary basal rate and turn on suspend before low function.
6. If there is unplanned activity and glucose is less than 5mmol/L, consider consuming some simple sugar before the start of activity.

Chapter 12: Tips for using an Insulin Pump and CGMS

Delivery of insulin

• Accurate carbohydrate counting and try to give meal bolus (5-15 mins) before every meal.
• Respond to alerts and prompts from the pump.
• Give a correction dose as instructed when having high glucose level.
• If a bolus is forgotten before meal:
  • Within 1 hour after eating:
    Enter half of the grams of carbohydrates eaten and recheck blood glucose after 2 hours. If glucose level is still high, enter the current blood glucose level and give the recommended correction bolus.
  • More than 1 hour after eating:
    Enter the blood glucose and give the recommended correction bolus.

Calibration of CGMS

• Depending on the model of CGMS: Some models require calibration at least 2 times a day (i.e. every 12 hours), preferably before going to bed and attending classes.
• Enter a blood glucose reading immediately for calibration and DO NOT calibrate when glucose level is fluctuating (e.g., after meals, after giving a bolus, during exercise).
• You can set a snooze to remind calibration later.
• You should calibrate before important activities (e.g., before an exam)

Before going to bed

• Avoid changing CGMS sensor and insulin infusion set.
• Calibrate CGMS before sleep.
• If glucose is on low-side (e.g. 4-5mmol/L before sleep), consider taking a small snack (5-10g) to prevent CGMS exiting from auto-mode.
• If glucose is high, consider correction bolus before sleep.

Travelling

• Bring your medical certificate for the use of insulin pump and CGMS, and notify security personnel and contact aviation authority.
• During hand/carry-on luggage examination, request the security personnel to visually inspect the equipment, do not send your devices through the X-ray machine.
• The whole body scanner could be a form of X-ray. Remove the sensor and transmitter prior to the scan or request an alternative screening process.
• Hand-carry all pump-related accessories, including sensors, transmitter, extra pump infusion sets/reservoirs and insulin etc.
• Bring extra insulin pens and pen needles (to be used at times of pump failure).
• Bring a cooler bag for storing insulin.
• Upon arrival, adjust the time of the pump to the correct time zone.

Chapter 13: Potential advantages and disadvantages of an Insulin Pump

Potential Advantages of an Insulin Pump:

• Fewer injections
• Flexibility
• Less hypoglycaemia
• Precision of insulin dosage
• Individualisation
• Better glycaemic control during illness or exercise

Potential Disadvantages of an Insulin Pump:

• Connection problems: Sensor glucose readings cannot be sent to insulin pump/mobile phone due to signal problem
• Risk of diabetic ketoacidosis: Due to pump malfunction, kinking, set dislodgement, tube blockage or bubbles
• Skin irritation and infection
• Frequent blood glucose testing
• Pain and fear of infusion set insertion
• High cost of insulin pump and accessories
• Medical wastes

Chapter 14: Message to parents:

Is an insulin pump right for my child? Yes or No

1. What does he / she think? Respect his/her decision!
2. Willing to be attached to the pump most of the time
3. Willing to do carbs counting
4. Willing to respond to alarms
5. Understand what pump failure is and its management

• Diabetes technology is not the solution for everything, pump / new technology might not be suitable for everyone
• Even with new diabetes technology, we should accept some imperfections in blood glucose control
• Insulin pump is just one of the treatment options
• Many children with diabetes can achieve good glucose control with traditional insulin injection regimen
• If an insulin pump is right for your child, please speak to your health professional / doctor to find out more

Jointly produced by

Endocrine and Diabetes Team, Hong Kong Children's Hospital
Youth Diabetes Action

Written by

Endocrine and Diabetes Team, Hong Kong Children's Hospital
Ms. Iris Poon
Ms. Candy Chan
Dr. Joanna Tung

Acknowledgment

Patients and families of Endocrine and Diabetes Team, Hong Kong Children's Hospital
HKU Medical Students:
Chan Ching Yan
Lo Ying Yan

Warm reminder: Technology keeps improving with time and there would be modifications in the future

January 2023